Telescopic instruments are widely used for magnifying a work area during precision work such as delicate surgery, dental work, inspection of circuit board solder joints, and assembly of miniature parts. A typical telemicroscopic instrument includes a pair of telemicroscopic loupes which are adjustably mounted to an eyeglass frame or headband. The telescopic loupes combine the long working distance of the telescope with the high quality magnification of the microscope. This type of optical instrument provides the user, a surgeon, for example, with a magnified image of the work area with a field of view at about an arm's length.
As one example, the ocular mounting assembly disclosed in U.S. Pat. No. 5,381,263 allows the mounting of a pair of ocular devices to an eyeglass frame, or head mount, and is linearly or rotationally adjustable through five degrees of freedom. An adjustable ocular support assembly with slidably extendable arms provides interpupillary distance, convergence angle and view adjustment of the ocular devices, which are rotatably attached to the support. An adjustable hinge/slide mount assembly is rotatably attached to the ocular support assembly and provides height and view angle adjustment of the ocular devices. When the slidable arms of the ocular support assembly are extended, however, some rotating motion may occur, in particular with heavier oculars and with fully extended support arms. The rotating motion causes vertical misalignment, or divergence, of the axes of the ocular devices. FIG. 1 shows the vertical misalignment between the axes of two ocular devices 14, when no stabilizers are included in the assembly housing 20. Excessive divergence can cause eyestrain, discomfort and even headaches.
U.S. Pat. No. 6,333,814, the entire content of which is incorporated herein by reference, improves upon the above design by providing a pair of stabilizers disposed inside the assembly housing and providing stability against rotational motion when the arms are extended. In one embodiment, the stabilizers are L-shaped, and can be either an integral part of the housing or bonded to it with adhesive. In an alternate embodiment, the stabilizers are interference-fitted balls, retained in position by retainer holes in the assembly housing, and receding into recess cut-outs at the end of the support arms when the arms are fully retracted. FIG. 2A is a top view and FIG. 2B an elevated view of part of this prior-art ocular mounting assembly showing the ocular devices 14, the supports arms 22 and the assembly housing 20. The stabilizing balls 70 are interference-fitted between the housing 20 and the slidable support arms 22 at diagonally opposite corners of the housing 20. The stabilizing effect is important when the support arms are extended outwardly from the housing. When the arms are fully retracted into the housing, the balls recede into recess cut-outs 72 at the ends of the support arms 22. FIG. 2C shows cross-section A-A of the assembly housing 20. The stabilizing ball 70 is interference-fitted between the assembly housing 20 and the support arm 22. The ball 70 is retained in place by retainer hole 74. The diameter of the retainer hole 74 is chosen to provide the desirable amount of interference fit. A large diameter allows the ball to move further into the hole, thus reducing the contact pressure on the arms.
Due to structure and operation of the ocular support arms described in the '814 patent, the design only allows for two stabilizing balls at diagonally opposite corners of the housing. The configuration is also physically bulky, limiting peripheral vision, for example, when the practitioner looks away from the loupes.
U.S. Pat. No. 7,791,798, the teachings of which are also incorporated herein by reference, describes a low-profile ocular mounting assembly wherein the top of each outwardly extending support arm is at or below the middle of the height of the housing. However, the support arms are received within the housing with sliding engagement on all sides, thereby preventing the inclusion of ball bearings or spacers to counteract twisting.
It would be advantageous to develop a mechanically stabilized optical mounting assembly that could accommodate more than a single pair of anti-twisting spacers. It would be further advantageous if the configuration was compatible with a low-profile design.